U.S. patent number 5,808,246 [Application Number 08/533,596] was granted by the patent office on 1998-09-15 for triac drive for three-phase line-powered linear induction motor elevator door operator.
This patent grant is currently assigned to Otis Elevator Company. Invention is credited to Edward E. Ahigian, David W. Barrett, Thomas He, Jerome F. Jaminet, Thomas M. Kowalczyk, Richard E. Kulak, Thomas M. McHugh, Richard E. Peruggi, Zbigniew Piech.
United States Patent |
5,808,246 |
Peruggi , et al. |
September 15, 1998 |
Triac drive for three-phase line-powered linear induction motor
elevator door operator
Abstract
An electronic motor drive produces a required motion profile for
an elevator door operator actuated by a three-phase, line-powered
linear induction motor (LIM) by means of an array of TRIAC switches
producing selected forces from the LIM. The TRIAC drive is capable
of producing acceleration, deceleration or free coast in either the
open or close direction of door operation. When controlled by an
algorithm such as a "time-optimal switch point" or "bang-bang"
control, the TRIAC drive produces the required motions from the
linear induction motor for elevator door operation. The motor
windings may be switchable between delta and wye hookups to provide
two distinct thrust levels. Phase angle modulation may be used to
provide finer control of thrust. The linear motor may be a 12-slot
arrangement having four poles and three phases and arranged with
flux emanating from the stationary primary (on the car) to a
stationary backiron part of the secondary also mounted on the car,
wherein the flux passes through a movable copper part of the
secondary attached to the elevator door and passing between the
primary and the backiron.
Inventors: |
Peruggi; Richard E.
(Glastonbury, CT), McHugh; Thomas M. (Farmington, CT),
Ahigian; Edward E. (Arlington Heights, IL), Jaminet; Jerome
F. (South Windsor, CT), He; Thomas (Unionville, CT),
Kowalczyk; Thomas M. (Farmington, CT), Kulak; Richard E.
(Bristol, CT), Barrett; David W. (Hartland, CT), Piech;
Zbigniew (East Hampton, CT) |
Assignee: |
Otis Elevator Company
(Farmington, CT)
|
Family
ID: |
24126652 |
Appl.
No.: |
08/533,596 |
Filed: |
September 25, 1995 |
Current U.S.
Class: |
187/316;
49/118 |
Current CPC
Class: |
B66B
13/143 (20130101); H02K 3/28 (20130101); H02K
41/025 (20130101) |
Current International
Class: |
B66B
13/14 (20060101); H02K 3/28 (20060101); H02K
41/025 (20060101); B66B 013/14 () |
Field of
Search: |
;187/316,317,289
;49/118,120 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
3264486 |
|
Nov 1991 |
|
JP |
|
1148444 |
|
Apr 1969 |
|
GB |
|
Other References
"Linear direct drives featuring three-phase asynchronous motors", a
brochure from Automation & Servo Technologies, Inc. a U.S.
representative of Krauss Maffei AG..
|
Primary Examiner: Nappi; Robert
Claims
We claim:
1. A linear induction motor (LIM) control for providing drive
current for driving a LIM according to a control strategy for
moving an elevator door, characterized in that said LIM control is
responsive to alternating current (AC) at a fixed frequency as
provided by a public utility, that said LIM control comprises a
plurality of switches connected at inputs thereof directly to said
AC and at outputs thereof directly to phase windings of said LIM,
that said switches are responsive to control signals provided
according to said control strategy for switching said phase
windings to constantly accelerate said door at full thrust for a
door open or close sequence until a first reference position is
reached by said door and then constantly decelerating said door at
full thrust until a second reference position is reached
corresponding to a substantially full open or closed door.
2. The LIM control of claim 1, further characterized in that said
switches are TRIAC switches.
3. The LIM control of claim 1, further characterized in that said
fixed frequency is 50 or 60 Hertz.
4. The LIM control of claim 1, further characterized in that said
LIM comprises a primary mounted on said elevator and a two-part
secondary comprising a steel plate first part mounted opposite the
primary of said LIM also mounted on said elevator and a copper
sheet second part mounted on said door and interposed between said
primary and said steel plate.
5. The LIM control of claim 1, further characterized in that said
control strategy is for alternately reversing two of said phase
windings to correspondingly accelerate and decelerate said door at
full thrust.
6. The LIM control of claim 1, further characterized in that said
switching is selected to occur between a starting point from which
said door is constantly accelerated to a switching point from which
said door is kept at a substantially constant velocity to a second
switching point corresponding to said first reference position from
which said door is constantly decelerated to said second reference
position.
7. The LIM control of claim 1, further characterized in that said
LIM control comprises an additional plurality of switches connected
to said phase windings for connecting said phase windings in a
delta or wye configuration in response, respectively, to a delta or
wye control signal, for selectively switching said configuration in
order to accelerate and decelerate said door at a selected one of
two distinct thrust levels.
8. The LIM control of claim 1, wherein each of said plurality of
switches is further characterized by
a zero crossing detector, responsive to said AC, for providing a
zero crossing signal indicative of said AC having a zero
magnitude;
a delay circuit, responsive to said zero crossing signal and to a
reference signal having a magnitude indicative of a selected delay
after detection of said zero magnitude, for providing a delay
output signal for switching one of said plurality of switches.
9. The LIM control of claim 1, wherein said plurality of switches
are responsive to said control signals for switching said phase
windings to decelerate said door either at said full thrust or by
coasting at zero thrust.
Description
TECHNICAL FIELD
This invention relates to elevators and, more particularly, to a
linear motor for actuating an elevator door.
BACKGROUND OF THE INVENTION
A linear door motor system for elevators is disclosed in U.S. Pat.
No. 5,373,120, assigned to Assignee hereof. That system used a
linear motor control for controlling a rotational torque that
varies with horizontal door movement (caused by a vertical force
exerted vertically by the linear motor acting through a
variable-length moment arm about the door's center of gravity). It
counteracts this rotational torque on the door by varying the
horizontal force for moving the door (caused by the linear motor
acting through a fixed-length moment arm about the door's center of
gravity). That motor control was eventually implemented by means of
an electronic variable voltage/frequency motor drive that runs at
10-20 Hz and 0-170 volts and is highly effective, especially for
high-performance elevator installations where a fast door open time
(e.g., one second) is demanded and where high component cost can be
tolerated, i.e., for the sake of high speed, reduction of noise (by
eliminating the need for mechanical linkages driven by a rotary
motor) and increased reliability.
The control strategy of U.S. Pat. No. 5,373,120 was, as shown in
FIG. 13 thereof, to use a quasi-elliptical velocity profile. This
was in contrast to the (simplified) "ramp up" and "ramp down"
velocity profile of the prior art electromechanical door operator
shown in FIG. 1 thereof. Naturally, it would be most advantageous
to be able to use the linear motor concept for lower-cost elevators
for the same reasons, i.e, replacing the old-style
electromechanical door operator. However, the cost of the
electronics, particularly the presently-implemented electronic
variable voltage/frequency motor drive, puts this innovation out of
reach for most new equipment installations.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a linear door
motor system for elevators using a different approach so that such
a system can be widely used for many different types of elevator
installations.
According to the present invention, a linear induction motor (LIM)
control for providing drive current for driving a LIM according to
a control strategy is responsive to alternating current (AC) at a
fixed frequency as provided by a public utility, and comprises a
plurality of switches connected at inputs thereof to said AC and at
outputs thereof to phase windings of said LIM, the switches being
responsive to control signals provided according to the control
strategy for switching the phase windings to at least accelerate
and decelerate the door. The switches may be TRIACs and the fixed
frequency may be 50 or 60 Hertz.
In further accord with the present invention, the LIM comprises a
primary mounted on the elevator and a two-part secondary comprising
a steel plate first part mounted opposite a primary of the LIM also
mounted on the elevator and a copper sheet second part mounted on
the door and interposed between the primary and the steel plate.
For purposes of the present invention, it should be realized that
other LIM configurations are possible, such as having the LIM
arranged as shown in U.S. Pat. No. 5,373,120, such as shown in
copending application U.S. Ser. No. (Atty Docket OT-2144), such as
the reverse of the above with the primary on the door and the
secondary on the car, or many others.
In still further accord with the present invention, the control
strategy is for alternately reversing two of the phase windings to
correspondingly at least accelerate and decelerate the door. The
switching can be selected to occur between a starting point from
which the door is constantly accelerated to a switching point from
which the door is constantly decelerated to a stopping point
corresponding to a substantially full open or closed door. Or, the
switching can be selected to occur between a starting point from
which the door is constantly accelerated to a switching point from
which the door is kept at a substantially constant velocity to a
second switching point from which the door is constantly
decelerated to a stopping point corresponding to a substantially
full open or closed door.
These and other objects, features and advantages of the present
invention will become more apparent in light of the detailed
description of a best mode embodiment thereof, as illustrated in
the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a linear door motor system for an elevator, according
to the present invention.
FIGS. 2a-2e show various instances of control strategies, some of
which are optimal, according to the present invention.
FIG. 3 shows a motor control, according to the present
invention.
FIG. 4 shows a linear motor primary with a winding arrangement,
according to the present invention.
FIG. 5 shows a TRIAC switch as implemented for control by a
microprocessor.
FIG. 6 shows the relation between FIGS. 6a, 6b and 6c, which
together show a motor control such as shown in FIG. 3 in detail,
using TRIAC switches according to FIG. 5.
FIG. 7 shows a delta-wye connection, according to the present
invention.
FIG. 8 shows the switches of FIG. 7 used for a wye hookup,
according to the present invention.
FIG. 9 shows the switches of FIG. 7 used for a delta hookup,
according to the present invention.
FIG. 10 shows a zero crossing detector circuit, according to the
present invention.
FIG. 11 shows the circuit of FIG. 10 used to achieve phase angle
modulation, according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a linear door motor system for actuating an elevator
door, according to the present invention. It differs from the
linear door motor system of U.S. Pat. No. 5,373,120 in using a
different motor orientation, a different computer control strategy
10, a different motor control 12 and a different linear motor
primary 14, all of which have been selected and designed so as to
make the concept more readily adaptable to elevator installations
of all types, particularly lower-cost elevator installations.
Given that the single most expensive item in the implemented linear
door motor system disclosed in U.S. Pat. No. 5,373,120 was the
motor control shown in FIG. 4 thereof, the motor control was
targeted as the single most important component in achieving a
cost-effective linear induction motor (LIM) driven elevator door.
The underlying idea of the present invention was to drive the
linear motor primary 14 directly from the AC supply line 16, by
means of the motor control 12 of the present disclosure, thereby
eliminating the relatively expensive drive described above.
However, such a configuration would not allow continuous control of
the thrust output by the LIM. Nevertheless, by utilizing a
time-optimal control strategy of bang/bang control in which the LIM
is made to apply full thrust to accelerate the doors, or full
thrust to decelerate the doors with the points of switching between
accelerate and decelerate determined by a setting of switching
curves, the desired powering of the LIM directly from the AC supply
line is achieved. The motor control 12 can use TRIAC switches to
accomplish the switching of the three-phase AC line 16. The linear
motor primary 14 is designed and optimized to operate at the
frequency of the AC mains, typically 50 or 60 Hz. This motor can be
made of two or more poles and one or more, e.g., three phases. The
LIM operates at high slip, so that it never approaches synchronous
speed and, as such, has the characteristics of a forcer, producing
an almost constant thrust over its entire normal operating
envelope.
As described in more detail below, the motor control 12 connects
the individual linear motor primary phase windings to the
appropriate phase or phases of the incoming AC mains 16.
The linear motor primary 14 is fixedly mounted to the elevator cab,
and a copper sheet part 18a of a linear motor secondary 18 is
mounted to a movable elevator door 20 while a ferromagnetic
backiron part 18b is mounted to the cab, such that thrust is
applied to the movable door when the primary is energized. Door
position and velocity are measured via a sensor 22, which may be
implemented as a linear optical strip mounted on the movable door
with a pickup on the cab.
As will be evident from FIG. 1, the linear motor has been oriented
differently from the orientation shown in U.S. Pat. No. 5,373,120,
where the primary was mounted above the door and the secondary was
placed flat on the top edge of the door so that a perpendicular
axis bridging the gap from the primary to the secondary is
vertical. According to the illustration of FIG. 1 hereof, the motor
is rotated ninety degrees so that the perpendicular axis bridging
the gap from the primary to the secondary is horizontal, rather
than vertical. It should be realized, however, that the invention
hereof may be used with any linear motor arrangement for driving an
elevator door.
A microprocessor may be employed to carry out the computer control
strategy 10, to read the sensor 22 and to respond to a command
signal on a line 24 from an elevator controller (not shown) for
providing switching commands on a line 26 to the motor control 12.
The computer control strategy 10 reads sensor signals on a line 28
from the sensor 22 and provides switching commands on the line 26
that result in current on a line 29 for full acceleration or
reverse current for full deceleration, depending on pre-computed
switch points, as described below.
The motor control 12, which may be implemented as a TRIAC
electronic switch circuit, thus applies 50/60 Hz line voltage 16 on
the line 29 to the linear motor primary 14 windings to effect the
commanded thrust. Status information may be provided back to the
elevator controller (not shown) on a line 30 from the computer
control strategy 10.
As shown in more detail in FIGS. 2a-e, the control problem is to
traverse the travel distance d in minimum time from a first
position (POS1) with zero velocity to a second position (POS2) with
zero velocity. The travel distance from POS1 to POS2 is known prior
to the start of door motion. Door position can be measured by the
sensor 22 of FIG. 1 and the velocity and/or acceleration derived
therefrom. The theory of time-optimal control specifies a bang/bang
control in which full acceleration, as indicated by an acceleration
profile 32 in FIG. 2a, is applied until a predetermined switch
point spt.sub.0, after which full deceleration is applied. It may
be assumed for purposes of the illustration that POS1 corresponds
to a door closed position and POS2 a door open position. A velocity
profile 34 corresponds to the acceleration profile 32. FIG. 2a
therefore shows spt.sub.0 as the time-optimal switch point, where
the door reaches fully-open position at zero velocity, i.e., it
exactly stops at that point. FIG. 2b shows a switch point spt.sub.1
that is later than spt.sub.0, so that the door still has a positive
velocity at POS2, as indicated by a velocity profile 36, while
still being decelerated as indicated by an acceleration profile 38
at the time of reaching POS2, at which point it crashes into the
stop. Obviously, switch point spt.sub.1 is not optimal and would
not be a good selection.
FIG. 2c shows a case where the switch point spt.sub.2 is earlier
than spt.sub.0, and the door reaches zero velocity as indicated by
a velocity profile 40 before reaching the fully-opened position.
Having thus stopped, it will begin going backwards if the drive
isn't shut off. Similarly, switch point spt.sub.2 is also not an
optimal choice.
FIG. 2d shows another optimal case where a switch point spt.sub.3 a
is just slightly earlier than spt.sub.0. As shown by a velocity
profile 42, the door stops at a position spt.sub.3b just short of
fully open. A second full acceleration is then applied to fully
open the door through a controlled "crash" into the stop, as
indicated by the velocity profile 42 and an acceleration profile
44.
FIG. 2e shows another optimal case with a pseudo-constant-velocity
portion of travel 46 made up of short acceleration/deceleration
bursts, as indicated by an acceleration profile 48. The
decelerations Can be replaced by an "OFF" state (for a longer time
period) with friction slowing the door down instead. As can be seen
by a velocity profile 50, the velocity is somewhat choppy but
relatively constant during the pseudo-constant-speed portion of
travel 46.
Turning now to FIG. 3, the motor control 12 of FIG. 1 is shown
carried out using an array of TRIAC switches 52a-e to produce the
desired forces from the linear motor. The TRIAC drive 12 is capable
of producing acceleration, deceleration or coasting in either the
open or closed direction of operation. When controlled by an
algorithm such as a "time-optimal switch point" or "bang/bang"
control strategy, such as shown in FIG. 2a, 2d or 2e, the TRIAC
drive produces the required motions from the linear induction motor
(LIM) 14 for elevator door operation.
The LIM 14 produces full thrust in a given direction (e.g., for
accelerating an opening door or decelerating a closing door) when
the three phase windings (motor coils) U, V, W of the LIM 14 are
connected in a particular manner to the three phases of the AC line
16. The LIM 14 produces full thrust in a direction opposite to the
given direction (e.g., for decelerating an opening door or
accelerating a closing door) by reversing the connections of any
two of the three motor phases to the AC line. On the other hand,
disconnecting the phase windings from the AC line allows the LIM
(along with the elevator door) to coast without producing thrust in
either direction. The motor control or TRIAC drive 12 uses TRIAC
switches 52a-e to accomplish the required switching function under
the control of the computer control strategy 10 of FIG. 1 by means
of control lines 26a, 26b, 26c.
FIG. 4 shows a winding pattern for a linear motor primary 14
implemented as a four-pole, three-phase primary. The wiring pattern
illustrated is connected as a wye-connected three-phase winding,
each winding spanning four slots with beginning (b) and ending (e)
leads connected as illustrated. The U1, V1, W1 leads are connected
to the corresponding U1, V1, W1 phase leads of FIG. 3 from the
TRIAC switch blocks 52a, 52b, 52d, respectively. A particular
embodiment of the linear motor primary 14 of FIG. 4 provides 95
Newtons of force using AWG 20 copper wire (0.813 mm outside
dimension), wherein each coil shown in FIG. 4 has 220 turns. The
overall length dimension for the primary of FIG. 4 is 170 mm, while
the width is 64 mm. The overall height (perpendicular to the plane
of the paper) is approximately 50 mm, while the slot length is 33
mm and is 8.6 mm wide.
The present invention is primarily concerned with the motor control
12 aspect of the linear door motor system disclosed herein for
elevators. However, copending application S/N (Atty Docket No.
OT-2033) addresses the linear motor 14, 18 of FIG. 1 itself in more
detail, especially as shown in FIGS. 5-11 and described at page 10,
line 31 through page 14, line 17, which is hereby incorporated by
reference for background, and separately claims aspects thereof.
Similarly, copending application S/N (Atty Docket No. OT-2114)
discloses a dual secondary linear induction motor which could be
used in lieu of the motor 14, 18 of FIG. 1 and which is hereby
incorporated by reference for background, particularly to FIGS.
1-10 thereof described at page 4, line 8 through page 8, line 15.
Other linear motors are usable as well, such as disclosed in U.S.
Pat. No. 5,373,100 in connection with FIGS. 2 and 3 thereof, at
column 4, line 27, through column 5, line 12, which is hereby
incorporated by reference for background. Finally, copending
application S/N (Atty Docket No. OT-2032) discloses in more detail
(in FIGS. 5-10 thereof as described at page 10, line 9 through page
24, line 20 thereof, which is hereby incorporated by reference for
background) the computer control strategy 10 of FIG. 1 and claims
such separately.
The problem addressed by the system of FIG. 1 involves the need to
electrically control a door operator that is powered by a linear
induction motor (LIM) designed to be driven directly from the
three-phase AC line 16. The LIM must be capable of producing
controlled motion in both the forward and reverse directions. The
drive 12 must be reliable, quiet and inexpensive. Typical
mechanical (relay) controllers do not meet these requirements for
noise and reliability.
An electronic motor control, according to the present invention,
provides the required range of motion profiles such as shown in
FIGS. 2a, 2d and 2e, for an elevator door operator actuated by the
three-phase line-powered LIM. The motor control or drive 12 of the
present invention uses an array of TRIAC switches such as shown in
FIG. 3 to produce the desired forces from the LIM. The TRIAC drive
is capable of producing acceleration, deceleration, or free coast
in either the open or close direction of door operation. When
controlled by an algorithm such as a "time-optimal switch point" or
"bang-bang" control, coupled with a velocity regulator, the TRIAC
drive produces the required motions from the LIM for elevator door
operation.
The LIM produces full thrust in a given direction (e.g., for
accelerating an opening door or decelerating a closing door) when
the three-phase windings (motor coils) of the LIM are connected in
a particular orientation to the three phases of the AC line. The
LIM produces full thrust in the opposite direction (e.g., for
decelerating an opening door or accelerating a closing door) by
reversing the connections of any two of the three motor phases to
the AC line. Disconnecting the motor phase windings from the AC
line allows the LIM (along with the elevator door) to coast without
producing thrust in either direction. The TRIAC drive uses TRIAC
switches to accomplish the required switching function.
FIG. 5 shows the TRIAC switch 52a of FIG. 3 in more detail, as
implemented for control by a microprocessor such as may be
contained within the computer control strategy block 10 of FIG. 1.
It should be realized that although the use of TRIAC switches is
disclosed herein, the principles of the present invention may be
carried out using any appropriate switch such as two anti-parallel
silicon controlled rectifiers, among others. The TRIAC switch 52a
of FIG. 5 is shown implemented as an optically isolated TRIAC
switch controlled by the control output on the line 26a from the
control logic or microprocessor of the computer control strategy
block 10 of FIG. 1. When the control signal on the line 26a is
driven to ground by the logic or microprocessor of the block 10 of
FIG. 1, electrical current flows from a voltage source (V.sub.in)
on a line 54, through a current-limiting resistor (R.sub.1) 56 and
to an optical isolator 58. The optical isolator 58 provides
electrical isolation between the control electronics in the block
10 of FIG. 1 and the high-voltage AC circuitry of the motor control
block 12. Other isolation elements, such as solid-state or
electromechanical relays or electronic switching circuits may also
be used for this purpose. The optically isolated TRIAC driver 58
includes a photodiode or phototransistor switch which controls a
TRIAC gate drive circuit which is switched "on" in response to
current flow in the optical isolator 58. This gate drive function
can also be achieved with discrete components, but the TRIAC driver
is used for convenience. The TRIAC driver switches gate current
"on" to a TRIAC (T.sub.1) 60 by conducting current from the AC line
phase on a line 16.sub.1 (as also shown in FIG. 3) through a
current-limiting resistance (here supplied by the combination of
resistors 62, 64 (R.sub.2, R.sub.3) to the gate of the TRIAC. This
turns the TRIAC "on", providing a very low resistance path for
electrical current to flow from the AC line phase, through the
TRIAC, to the motor phase winding (U1). A capacitor (C.sub.1) 66
can optionally be used as a snubber to protect the TRIAC driver
from switching transients. Likewise, a block (S) 68 is an optional
snubber circuit which can comprise a capacitor and resistor in
series and that can be used to protect the TRIAC itself from
switching transients. Another optional component, a resistor
(R.sub.4) 70, can be used to vary the sensitivity of the TRIAC
gate. Once triggered, AC current will flow through the TRIAC as
long as gate current continues to be applied. When the gate current
is removed, current continues to flow until the AC voltage of the
particular line phase goes to zero, at which point the TRIAC
switches off.
FIGS. 6A, 6B and 6C fit together as shown in FIG. 6 and together
show the motor control 12 of FIGS. 1 and 3 in more detail. As can
be seen in FIG. 6A, the TRIAC switch blocks 52a, 52b, 52c, and in
FIG. 6B, the TRIAC switch blocks 52d, 52e, are shown implemented in
detail according to the above-discussed details of FIG. 5. FIG. 6B
shows in a lower portion thereof, a circuit 70 which represents an
additional AC switch, and FIG. 6C shows a circuit 72 which
represents a DC switch. These circuits 70, 72 may be used to
energize an AC or DC (respectively) solenoid for the purpose of
providing an electrical control means available to brake the door
with an electromechanical braking device (not shown), or to control
another electromechanical device (not shown) that couples the
elevator car door to the hoistway door.
Referring back to FIG. 3, a description of the forward/reverse
TRIAC switch arrangement operation follows. As described previously
in connection with FIGS. 3 and 4, the LIM may comprise a
three-phase motor with the motor phases being arbitrarily
designated as phases U, V and W, and which can be connected in
either a wye or delta configuration. It is, of course, noted that
the designations of phase 1, phase 2 and phase 3 in FIG. 3, as well
as their relation to the LIM phases U1, V1 and W1, are completely
arbitrary. The LIM is driven in one direction by applying (driving
to ground) control lines 26a, 26b, which results in LIM phase U
being connected to AC line phase 1, phase V to phase 2, and phase W
to phase 3. The LIM can supply thrust in the opposite direction by
applying control lines 26a, 26c, resulting in LIM phase U being
connected to AC line phase 1, phase V to phase 3, and phase W to
phase 2. The diodes D1 and D2 prevent the TRIACs from shorting AC
line phase 2 to phase 3 in the event that both control lines 26b
and 26c are inadvertently turned "on" at the same time. If control
lines 26b, 26c were both turned "on" at the same time, the
arrangement of the two diodes would result in both LIM phases V and
W being connected to the same AC line phase (shown here as phase
3), inhibiting door motion as well as preventing the shorting of
the AC line phases. When all three control lines 26a, 26b, 26c are
turned "off", no electrical power is applied to the LIM, which will
then coast, slowing down due to frictional losses.
As will be appreciated, this arrangement of TRIAC switches allows
the door to be controlled by means of a simple control mechanism.
As implemented, the control comprises an algorithm contained within
the computer control strategy block 10 of FIG. 1, which may be
implemented as a microprocessor with software, as disclosed in
copending S/N (Atty Docket OT-2032). This algorithm uses control
loop position (and closed loop velocity derived from the position
feedback) to control the state of the TRIAC switches. A set of
electrical or electromechanical switches at appropriate positions
along the path of door travel could accomplish a similar function
but would not be robust. The microprocessor implementation of the
control strategy accelerates the door in the desired direction of
travel, until either a desired velocity is reached or until a point
is reached at which the door must begin to decelerate to stop at
the desired point. The acceleration and deceleration is controlled
by setting the appropriate state of the control lines 26a, 26b, 26c
of FIG. 3. A constant velocity state is achieved by either
alternately switching from an acceleration condition to a
deceleration condition, or switching between acceleration and coast
conditions, at a frequency typically between two and twenty times
per second, which maintains the door speed within a velocity band
that approximates a constant speed. At the end of travel, the
control maintains the door velocity at a sufficiently low level
that the door can contact a mechanical stop to terminate
travel.
The basic TRIAC switch block as shown in FIG. 5 can be used in
various other arrangements to achieve additional LIM control modes
of operation. The basic accelerate-coast or accelerate-decelerate
technique of running at a constant velocity can be improved upon by
adding TRIAC switches to both sides of each of the motor windings,
such that not only can the phase connections be reversed, as
before, but now the motor windings themselves can also be connected
as either a wye or as a delta configuration. Such a setup produces
two discrete thrust levels in each direction, as well as the coast
or "off" state. This allows the control to add a high thrust-low
thrust state to control constant speed.
For instance, FIG. 7 shows a plurality of switches 74, 76, 78, 80,
82, 84, each of which may be similar to the TRIAC switch shown in
FIG. 5 for controlling the hookup of three motor windings U, V, W,
according to a control signal "control delta" or "control wye".
Terminals U1, V1, W1 of the windings U, V, W will be hooked up to
the TRIACs 52a-52e of FIG. 3, as before.
As suggested above, the intent of the "delta-wye" controllable
hookup is to allow the coils of the motor, such as the linear
induction motor primary windings of FIG. 4, to be connected in
either a "delta" or a "wye" configuration, under the control of the
computer control strategy block 10 or the elevator controller
(which may incorporate the computer control strategy or be separate
therefrom). The impedance of the motor will change depending on
whether it is connected as a "delta" or "wye". This will alter the
current flowing through the motor coils, causing different thrust
or force levels (for a linear motor) or different torque levels
(for a rotary motor) to be produced by the motor. Although six
switches 74, 76, 78, 80, 82, 84 are shown in FIG. 7, five can be
adequately used for this purpose. One of the switches 74, 76 or 78
can be optionally eliminated, replaced by a hard-wired connection,
since the combination of the other two switches being turned off
effectively isolates the third coil.
When the "control wye" control line is activated, one side of each
of the three motor coils is connected to a common point 86, setting
the coils in a "wye" configuration, with the other side of each
coil connected to the appropriate linear induction motor phase, as
shown in FIG. 8, to the appropriate linear induction motor phase
drive output from the motor drive 12.
When the "control delta" control line is asserted, the coils are
hooked up as shown in FIG. 9, and each side of each motor coil is
connected to an appropriate motor drive output to form a "delta"
configuration. As with the control 2 and control 3 lines in FIG. 3,
the "control delta" and "control wye" control lines can be
diode-coupled to preclude asserting both at the same time.
Also, as an additional improvement, a "zero crossing detector"
circuit 88, such as shown in FIG. 10, can be added along with a
comparator to each of the TRIAC switches in order to permit a
continuously-variable thrust to be developed in the LIM by a
technique commonly known as "phase-angle modulation". This
technique turns the TRIAC "on" for only a portion of each
half-cycle of the AC line cycle, e.g., 120 times per second for a
60 Hz AC line. The TRIAC remains in conduction until the end of the
half-cycle, at which time it turns "off" until triggered again in
the following half-cycle. The earlier within the half-cycle that
the TRIAC is triggered, the longer the TRIAC remains "on",
producing greater amounts of thrust from the LIM. The switching
point is determined by a reference signal 90 relative to either a
time delay 92 following the zero crossing of the AC line, or a
voltage level of the AC line (for conduction angles greater than 90
degrees) following the zero crossing. This variable LIM thrust is
obtained in either direction by switching the phasing of two of the
LIM phases as before. The "phase-angle modulation" technique
provides for a smoother closed loop control of the door motion
profiles, at some increase in complexity, than the other techniques
described above.
The control circuit of FIG. 10 comprises the zero crossing detector
88 that senses when each half cycle of the AC line reaches a level
near zero volts, as shown at points 94 of FIG. 11 (the zero
crossing point). This starts a delay circuit 92, which will
generate a delay (shown as a delay angle 94 in FIG. 11) based upon
the reference input on the line 90 supplied by the elevator
controller (not shown), the computer control strategy 10 or the
like. After the delay period is over, a TRIAC trigger circuit 98
will generate a trigger pulse 100 that turns the TRIAC on to a
conducting state 102 so that the voltage is not applied to the
motor during the delay period 96, and voltage is applied to the
motor during the conduction period 102. A separate control circuit
is required for each of the three AC line phases. As the motor
drive varies the reference input to the delay circuit, the control
circuit varies the delay angle and hence the delay period 96,
changing the average voltage applied to the motor and thus varying
the motor output. As the delay (and therefore the delay angle)
increases, the conduction angle is reduced, resulting in a lower
average voltage applied to the motor and lower thrust or force
output. Conversely, decreasing the delay results in a higher
average voltage and greater motor output.
Although the invention has been shown and described with respect to
a best mode embodiment thereof, it should be understood by those
skilled in the art that the foregoing and various other changes,
omissions and additions in the form and detail thereof may be made
therein without departing from the spirit and scope of the
invention.
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